Rational self inserts are well-written self inserts solely because they don't break reader's immersion. You self-insert yourself into the SI fanfic imagining what would you do in the self-insert's shoes. They need to be realistic. We need to be realistic. Think about it. You are reading a story where a guy is reincarnated/transmigrated to a foreign universe and the first thing they do is freak out. That's good. That is a normal human reaction from getting cosmically kidnapped from one world to another, especially a fantasy world you read manga about. But the next thing they do defines whether the self insert fanfic is rational or not, or I would like to say whether the fanfic is well-written or wish fulfilment trash.
Does the self insert...
Have fun carelessly exploring and trying out their new magical powers?
Plan on meeting and befriending the canon characters?
Instantly befriend the main canon characters through their apparent godlike social skills?
Easily create a harem with their reincarnated good looks or otherworldly transmigrated visage?
Instantly become a genius in the mystical arts without no hard training whatsoever?
Constantly allude to knowledge and idiom they should not have and better yet, with the canon characters not questioning, calling out, or noticing this strange behavior?
Save someone that they know is going to die if they don't do anything without thinking of the butterflied consequences?
Congratulations. If the self insert fanfic you are reading answers yes to one or two of the following questions the SI you are reading is not rational. It's wish fulfilment trash.
The next realistic and rational thing the self insert should do is Survive. The self insert should plan and secure their survival. This is their new life now. This is our new life now. This is not a game or one of the mangas we read pre-insert. The fiction you and the self insert read is now reality and we should treat it as such. If the SI was reincarnated, they don't have to worry as much compared to being inexplicably transmigrated. They have no identity, money, and shelter so they better be taking their situation seriously. It is after-all, our new life now. And if the SI got where they were by a ROB(random omnipotent being), I wouldn't be reading that Self-insert fanfic anyway because ROBs are trash and they ruin stories.
I know I sound Hypocrite because ny mc is also send my a ROB but this ROB is very essential for my later plot( 50 chaps or so. ), Its not like I'll give him a small screen time.
I have no problem on Wish fulfilment tbh because I know they are novice writers that wanted to be free by themselves.
but Im just tired that Im reading below average Fanfictions.
Please do not be offended by my words.