Not sure to what depth of decisions you're talking about, but it sounds like low-impact stuff if they're instant. The vast majority of decisions made throughout the day have no real impact on your life in any measurable way.

I like a dumpling restaurant near me. I pick anything in my top 5. Why not #1? Because I don't know which is the best dumpling. I can spend an hour trying to perfectly gauge my mood against their offerings, or I can settle for, potentially, 5th best in one minute. That's #5 out of 40. If you ask me why I chose that particular type, I'll say I don't know, and then formulate my inner thoughts into a coherent sentence. It's not lying, it's just translating feelings into words. Feelings that represent a decision that will likely not affect my life. The important decision was to eat, not find the #1 dumpling. Plus, yes, it's nice to give yourself reassurance that you made a good decision. Again, it's not lying to yourself to make yourself believe it, it's reminding yourself that you made a fine decision. It's decided, so you may as well seek the benefits. If it's the wrong decision, you can't undo it, but you can make new decisions to change course.

How often do you make wrong decisions as opposed to simply less-than-the-best? Probably pretty rarely. Sure, there could be larger school or career choices, but you have no way of knowing how life would have played out on the other path. Maybe you'd make more money, or maybe you're only seeing the highlights reel from someone else. Maybe your current path is hitting a dead end, but maybe the other path included the worst manager of your life. Maybe you got stuck in surprise traffic, but maybe you avoided being part of another accident. Life moves forward and you're still walking.

If you find yourself dwelling on every decision, taking too long to decide, second guessing it after committing, and then feeling regret that there was a better option despite fulfilling your actual need, those aren't pensive thoughts. That's probably anxiety.