Learn Turkish: Gecikmenin sebebi trafikti, ben taksi bulamadım. - The reason for the delay was traffic, I could not find a taxi.

The root is bul- (to find). To show inability, we add -ama (or -eme) right after the root. Here, bul- takes -ama, becoming bulama-. Then we add the past tense -dı and the "I" ending -m, giving us bulamadım (I could not find).

Why is it sebebi instead of sebep?

Sebep means "reason." The phrase "reason for the delay" is a possessive connection in Turkish: gecikmenin (the delay's) + sebep + -i (its). When we add the vowel-starting suffix -i to sebep, the hard p softens to a b, making it sebebi.

What is the -ti doing at the end of trafikti?

It is the past tense ending for nouns, meaning "was." The word is trafik (traffic). Because trafik ends in a hard consonant (k), the standard past tense suffix -di changes to -ti to match it, forming trafikti (was traffic).

Why do we use the word ben here if bulamadım already means "I could not find"?

You are right that bulamadım already includes "I" because of the -m at the end. Using ben is optional, but it is often used for emphasis or contrast. Here it emphasizes your side of the story: "The traffic caused the delay, and as for me, I couldn't find a taxi."