When should you FF: Analysis
https://www.leagueofgraphs.com/rankings/win-stats
According to the stats getting giving first blood, makes you lose 60% of the time.
Giving herald makes you lose 70% of the time.
Giving first drag makes you lose 69% of the time.
Giving first Baron makes you lose 82% of the time.
Giving first inhibitor makes you lose 91% of the time.
Giving first brick makes you lose 71% of the time.
Now assuming you belong in your mmr is soft capped already, you should have a 50% win rate. That means even if you lose this game, by the law of large numbers, your subsequent games will work out to give you the same mmr. Why waste your time playing a lost game when you can ff and move onto the next one?
The average games takes about 25-30 minutes. Refusing to ff 20 when you're an inhib down would give you a 1/10 chance of comeback. In ten games in the same situation, you'd lose 50-100 minutes and if you gain 15 lp per win, you'd be losing 135 LP. If you FF 20, you'd save 50-100 minutes, losing 150 lp. With the time saved, you could have played an extra 3-4 more games and could cut your loses down from 150 lp to 90 lp.
Going back to our numbers, giving either baron or inhibitor should be grounds for ff20. You should not ff if your team gives first blood. Giving first brick + drag + herald should ff. Giving first brick + drag + herald + blood should ff. Giving 2/3 of the 70% firsts and blood should ff. Giving 2/3 of the 70% but taking blood and or baron or inhib should continue to play.
Remember, your never give up attitude won't win games. Stats don't lie. You can only make a comeback if the other 4 people isn't tilted and willing to play on.