がち

A lot of/Tendency to happen (Negative)
ます stem + がち
Noun + がち (Rare)

がち is a な adjective that attaches to the ます stem of a verb.
It indicates that something often happens, or there is a tendency for it to happen.
This can be used about an individual, or as a generic statement. 

がち is only used for negative things.

In very rare cases, it may come after a noun (it must be a noun you might use になりがち) with.

• やりがちなミス
  A common mistake. (A mistake likely to be made)
  
  
• ありがちな問題
  A common problem. (A problem apt to exist)
  
  
• 冬は太りがちな時期だ
  Winter is a time when people are apt to get fat. (tendency/often)
  
  
• 親は心配しがちな存在
  Parents are existences that are apt to worry. (often worry)
  
  
• 病気がちな人
  A person that is apt to get sick (often sick). (practically the only Noun + がち I could find)
  
  

Notes

• Although you may see 勝ち, it is almost always written as がち
• 早い者勝ち is a different kind of がち (Meaning win).