This is the 51st most frequent Finnish word.
itse
"Self" or "oneself."
Here, 'itse' emphasizes that the subject is performing the action personally, without assistance or substitution.
Teen tämän itse.
I will do this myself.
In this context, 'itse asiassa' is a phrase meaning 'actually,' and 'itse' is part of an idiomatic expression.
Opin tästä itse asiassa paljon.
I actually learned a lot from this.
In this sentence, 'itse' specifies that the subject is the one who completed the task.