So, kind of like real life. How many high school varsity sports players quickly discover that despite being good in HS, they are at best, walk on quality for the college team? Same for the cheer squad. And that HS valedictorian is a middling academic in college. Plus there is the ever present, "I found something I like doing better then X."So my basic problem with elaborate character backstory creation, which is why I tend to not enjoy lifepath systems and heavy-handed character creation prompts, is that at the outset I really don't know this character I haven't played yet, and whatever is created at the outset rarely really jives with who the character ends up being. I don't know how they will behave in the campaign, how they will gel with the other characters, or what their story in our shared narrative is going to be. Sure I don't mind starting with some character prompts to get the roleplaying going, but, when games allow, I now tend to fill most of the backstory in after I've played a few sessions and have a clearer idea of who the character actually is in the campaign.
Which is all to say for me to get behind a lifepath system like this the "fill in the lifepath and act out flashbacks" session would be after the third level-up or something, and then the flashbacks could be events that tie into who the character actually is, rather than who the player thinks they want them to be before they've played them.
Backstory is just that, the past. What the character does next is determined by how the player plays it. But the backstory can provide some useful info for how to start playing the character. That HS softball star that can't make the college team may still make use of softball skills once hired on with a company that engages in softball games with other companies. Or that character that did a lot of sailing in childhood may find those skills useful if the cargo ship providing passages sinks and the character is left with others in a lifeboat.
Backstory avoids the problem of "What did your character do before being here?" being an unknown. It doesn't define what the character does next.

