ichidan verb
overthink; think too much; worry excessively
Used when someone dwells on a problem, reads too much into a situation, or is overly concerned. Often carries a negative nuance of unnecessary worry.
彼はいつも小さなことを考えすぎる。
He always overthinks small things.
考えすぎると、かえって失敗するよ。
If you overthink it, you'll actually mess up.
Standard kanji spelling.
Variant using the kanji 過 for the auxiliary verb すぎる.
考え込む means to be lost in thought or to brood, often with a nuance of being unable to stop thinking. 考えすぎる focuses more on excessive thinking that leads to worry or poor decisions.
Compound of 考える (to think) and the auxiliary verb すぎる (to do too much).