An ideal person or a person who knows how to handle money well set a goal to stop.
yes the ideal logic is 2x your salary.
1x means you can stop working and still get your income
1x for the new things you want to do with the new free time you have
but sometimes logic can surprise you.
once getting this logical 'contented' amount of 2x. your aspirations then raise up a level and your new higher level requires new standards and thus new income level.
EG
when your 20 you think if you can just get $300/w (~$7.50x40) then you just dont need to find a minimum wage job to survive,
bu then having that no-work lifestyle. and being 20. you want to hang out at bars and impress women. so you start spending more than you would if you were working and just going home each night.
so now you want $600/week(your 20yo ideal contented 2x lifestyle)
then at 21 you settle down with a woman and decide to get serious. marriage/kids. and suddenly more income is needed.
($10k wedding booked in 6 months needs over $400 a week saved up)
heck a $2400 a month wont pay all the bills and afford you a 3bedroom family home
after all your 20yo life only cost you $50 in food. but now your paying out $200 in food for you, wife and 2 kids. your electric and water has increased 4x too due to your family. so suddenly $1200 a week feels the same as $300 when you were single.
so yea maybe you think if you had $3600 a month, you can have $1200 a month extra spare cash. but that will only get you a $200k mortgage over 15 years. not exactly gonna get you a nice place you want to have your kids raised up in.
so when you were 20 thinking $300/w would be enough. a couple years later suddenly $900/w($3600/m) aint enough
$300/w might be ok if your content on being single all your life
but i guarantee you this. calculating a content life at 20 wont be a content life at 30