Used to describe a general tendency, often with a negative or undesirable outcome. Followed by a verb phrase.
People tend not to notice their own flaws.
When you're busy, you tend to forget important things.
Kana spelling is common and avoids potential confusion with the kanji 得.
Derived from the verb 得る (える, 'to get') in its classical 連用形 (continuative form) 得 (え) + particle て + verb する, literally 'getting and doing', which developed into an adverbial expression meaning 'tend to'.