Densha no naka ni kasa wo wasurete shimaimashita.

I accidentally left my umbrella in the train.

Tomodachi to no taisetsu na yakusoku wo sukkari wasurete ita.

I completely forgot about the important promise I made with my friend.

Kanji no kakikata wo wasurenai you ni, mainichi renshuu shite imasu.

I practice every day so that I won't forget how to write kanji.

Shukudai wo dasu no wo wasureta koto ni, gakkou ni tsuite kara kizukimashita.

I realized after arriving at school that I had forgotten to hand in my homework.

Ano utsukushii keshiki no koto wa, isshou wasurenai deshou.

I will probably never forget that beautiful scenery for the rest of my life.

Saikin, hito no namae wo wasureyasuku natte komatte imasu.

Recently, I've been having trouble because I tend to forget people's names easily.