I think the previous point on W&B is well made and applies to any a/c.
Like quite a few PPL's I flew the same rented 172 for a while on trips to Le Touq and Calais etc. If it took 4 people and some booze with full tanks last week, then it's going to be the same this week.....
It was only when I had my first owned a/c, a TB9 that I started to do W&B properly. I'm ashamed to say I would not have thought twice about loading her up and setting off but the guy I bought it from sent me a spreadsheet with W&B on it as an afterthought.
I was confused at first because I just couldn't get the figures to add up properly.
Slowly it dawned on muggins that they were adding up properly and the answers were absolutely correct. The margin of error on 4 seater light a/c is stunningly small and I wonder how many PPl's have that fact drummed into them during training?