You're sitting at 25nl at PokerStars for the first time since moving up from 10nl, and you're 8-tabling. You're dealt AA and it folds to you on the button. You make your standard 4x raise, and the BB calls. After a good run of cards, you have $150 and the BB has you covered. The flop comes A95 rainbow. The BB open shoves with QQ and you call. The turn is a Q and the river is a Q. You realize that this is nearly the worst possible beat (based on your equity when the money went in) that you can take in no limit holdem (you were a 99.899% favorite on the flop). Immediately after the Q hits the river, you have critical decisions to make on three of your other tables.

What does this have to do with walking through traffic?

First Edit:

You're walking down the sidewalk approaching the crosswalk at an intersection. You look around and don't see anything coming. As you start to walk across the street, a bicycle comes barreling towards you and turns at the last second to barely miss hitting you head-on, but gives you quite a bump. How would you honestly react?

Second Edit:

The guy on the bicycle speeds away immediately after hitting you. What happens if you turn to him and start yelling?

Third Edit:

You get smashed by a cab that you would have seen coming if you wouldn't have lost your cool.

This is a somewhat dull analogy sort of thing that most people will read and at first glance know exactly what the analogy means and what the lesson seems to be, but they'll miss something bigger. Although this is a rather blown-up example, things that happen every single day of your life that have become habit affect your poker game, and vice versa.

When working on tilt control, you're also learning about keeping your cool when something goes wrong in the "real world", or anything else that you enjoy doing for that matter.

One has to investigate the principle in one thing or one even exhaustively... Things and the self are governed by the same principle. If you understand one, you understand the other, for the truth within and without are identical.
-Er Cheng Yishu, 11th century