がち 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.
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ここに来（く）るといつもパフェを頼（たの）みがちだけど、今日（きょう）はパンケーキを頼（たの）む。
When I come here I always tend to order parfait, but today I am getting a pancake.
うちの子（こ）は病気（びょうき）がちなので、週（しゅう）に二（に）、三（さん）日（にち）ぐらいは学校（がっこう）を休（やす）みます。
My son tends to get sick a lot, so he will take 2 to 3 days off of school.
サボりがちな人（ひと）はだいたい成績（せいせき）が悪（わる）い。
People who tend to skip school usually have bad grades.
がち 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.
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暇（ひま）なときはテレビを見（み）がちだけど、忙（いそが）しい時（とき）には全然（ぜんぜん）見（み）ない。
Watching TV wins out when I am bored, but when I am busy I don't watch it at all.
俺（おれ）が回（まわ）すと当（あ）たりがちだから、俺（おれ）にやらせてみろ。
Hitting the jackpot wins out when I spin it, so why don't you let me do it.
釣（つ）れないことはありがちだから、落（お）ち込（こ）まなくてもいいよ。そういう日（ひ）もあるさ。
Times that you cannot catch anything often win out, so don't be so upset. It happens.