A phrase used when something may be caused by a particular reason but there is uncertainty — often appears as '...のせいか' meaning 'perhaps because...'.
寝不足のせいか、今日は頭が重い。
Maybe because I'm sleep-deprived, my head feels heavy today.
年のせいか、最近物忘れがひどい。
Perhaps because of my age, I've been forgetting things a lot recently.
雨のせいか、試合は中止になった。
Maybe because of the rain, the match was cancelled.