ひとつ…できない => cannot do the bigger things N3
Ability
~Vた + せつな => moment, instant, juncture N1
Beyond expectations
させて[頂「いただ」]きます/させてもらいます => Allow me to A N1
Miscellaneous
せいで/せいか => Because of A, B N3
Reason, Result, Response
せいか => perhaps because ~ N2
に越したことはない => It’s best that, There’s nothing better than ~ N2
いつかの ... => Previously N4
Time
きらい => Hate... N5
Ability
せいにする => Blame... N2
Cause, reason
につき => due to; because of; per; each N2
つきましては => about; concerning; regarding N2
Cause, reason
~つい      => accidentally; unintentionally; by mistake N3
Regret