Be a little bit more trusting than most people think sensible

I do hope you asked some particular person to watch your bag for you, which dramatically cuts down on the probability that someone would steal it: ordinary people really do take such an assignment seriously, so you'd be reducing the chances from "someone in the bar is a thief" to "either this particular person is a thief, or this particular person is indifferent to social expectations and someone else is a thief".

One day I hope to not even have to persuade myself, but meanwhile I notice my prediction was correct and feel just a little bit pleased with myself.

Could use the same reasoning when predicting you won't be having a car accident, then being pleased not having bothered with your seatbelt.

When you're unsure if an event is rare or really rare, noticing that an event did not occur in a few specific situations won't much differentiate rare from really rare, since it's the expected result in both cases.

The way I would approach this is with math, because humans are bad at probabilities.

What are the odds of your stuff getting taken? One in a hundred would still be compatible with 'nothing happened the last hundred times', and one in a hundred is probably a reasonable estimate. Let's go with one in five hundred, since you're feeling lucky.

You have two thousand pounds of stuff in your bag, which would disappear if someone took it. Simply multiply to get the expected loss: 0.002*2000 = four pounds. You trip to the loo cost you four pounds. (If the odds are actually closer to one in a hundred, your trip cost you twenty pounds instead.)

If you're ok with paying four pounds to go to the loo bag-free, then hey, victory is yours.

But remember that you are playing a lottery here, and that it's a net monetary loss in the long run. If your time/effort tradeoff is worth the money then so be it, but make that decision consciously and based on data. Do not try to 'gut feel' your way around probabilities of less than one in fifty.

This reasoning reminds me a bit of Umesh Vazirani -- "If you’ve never missed a flight, you’re spending too much time in airports."

If your stuff has never been stolen, you're spending too much time/effort/money guarding it.

So if I'm in a coffee shop with a laptop, and I think I'll have to hunt around for a seat if I give mine up, I'll ask someone to watch my laptop. It's way less than $5k in value, but it's also both easier to steal and more obviously worth stealing.

About "how trusting should I be", I would like to quickly bring up a bit of the scientific research. I've read a bit of this, and have concluded in high certainty that individual trust gives off a decent positive externality.

Quite a bit of econometric research (yea, it's not the best, but it's what we have) shows that positive levels of trust correlate with higher economic growth.
See: http://oep.oxfordjournals.org/content/56/1/118.short http://onlinelibrary.wiley.com/doi/10.1111/1468-0297.00609/abstract

However, I very much remember reading about how entrepreneurs have lower trust levels than most people on average, but can't seem to find the paper right now.

What I'd imagine is that in general trust helps society, which makes a lot of sense as it allows trade to function. However, it may very well be that the level of trust optimal for an individual is quite lower than that optimal for his or her society. Makes sense if trust is looked at similar to altruism.

In this case, obviously the more trust people have with other people and their bags, the more cases of stealing that will occur. On the whole this may help your surrounding people, as some of these will benefit from stealing. However, the disadvantage would come to yourself at the expected cost of having your stuff stolen.

It would be interesting to factor in not only how much your bags being lost would cost you, but how much they would benefit the person who steals them.

I've got trust issues.

It helps me to clearly identify the potential cost involved should the trust be betrayed. "Ok, that's the loss, I'll live." I also try to inject some priors for the person I'm dealing with - not what they could do, but what they are likely to do.

I've concluded that I've missed far more in opportunities than I've made up for by avoiding betrayal. Life isn't so hard. I try to remind myself of that.

I grew up in New York City in the 1980s which was a high-crime period. I was personally subject to a fair amount of property theft, and became very sensitized to these issues. After moving out of NYC, and getting older, and crime in the US dropping in general, I let go of some anxiety around theft. However, there are some very minor things that help me.

For example, if I ride my bike to a coffee shop, I'll leave outside unlocked, but in view through the window and flip it over on its seat and handlebars. Or thread my helmet strap through the wheel.

My feeling is that little things like that will reduce the likely hood of theft.

Likewise, if I leave my laptop (in a laptop bag) in my car for a bit, I'll throw a jacket over it.

A while back here a few people revealed they were Mr Money Mustache fans. One of the more intriguing blog posts of his I read touches on this topic

http://www.mrmoneymustache.com/2012/06/11/get-rich-with-trust/

I had a similar experience in an LA pub while waiting for my flight out. I asked a couple that was sitting nearby to watch my stuff, and they were kind enough to do so. Less risky than what you did, but still a calculated risk.

I don't think that it's a good idea to use other people behavior as reference. The proper way to handle the situation is to do an utility calcualation.

How likely is it that something gets stolen?

I would guess that the average person has some instances where they trust too much and others where they trust too little. People in general put little trust in strangers but much more trust if they "know" the person. In reality getting to "know" a person doesn't change them. A lot of crimes aren't done by strangers but by acquaintances.