weak-willedDescribes someone who has difficulty resisting temptation or sticking to decisions. The phrase modifies a noun, such as 意志の弱い人 (a weak-willed person).
JA: 私は意志の弱い人間なので、ダイエット中でもお菓子を食べてしまう。
EN: I'm weak-willed, so I end up eating sweets even when I'm on a diet.