is a suffix in Japanese that will be used after nouns, or the 連用形（れんようけい） (conjunctive form) of verbs. It conveys that someone is ‘apt to (A)’, ‘tends to (A)’, or ‘is prone to (A)’. Although not always negative, がち
is most frequently used to express negative tendencies.
When I come here I always tend to order parfait, but today I am getting a pancake.
My son tends to get sick a lot, so he will take 2 to 3 days off of school.
People who tend to skip school usually have bad grades.
as a grammar structure comes from the word 勝（が）ち, meaning ‘a win’. 勝（が）ち in itself is used to express something that appears ‘repeatedly’, or ‘again and again’. Due to this, がち
may be thought of as similar to ‘to win out’ in English, meaning that ‘although there are many possibilities, (A) winning out is the most likely’. This ‘winning out’ may be due to preference, or sheer good/bad luck.
Watching TV wins out when I am bored, but when I am busy I don't watch it at all.
Hitting the jackpot wins out when I spin it, so why don't you let me do it.
Times that you cannot catch anything often win out, so don't be so upset. It happens.