This is the 25th most frequent Arabic word.
لكن
"لكن" means "but" or "however."
لكن here is used as a conjunction to introduce a contrast between the desire to go out and the unfavorable weather condition.
أردت الخروج، لكن الطقس كان سيئًا.
I wanted to go out, but the weather was bad.
لكن introduces a contradiction between positive qualities and occasional random behavior.
هو ذكي ونشيط، لكن أحيانًا يتصرفُ بعشوائية.
He is smart and active, but sometimes he acts randomly.
لكن expresses a contrast between the lack of understanding and the intention to keep trying.