3:165

Why [is it that] when a [single] disaster struck you [on the day of Uhud], although you had struck [the enemy in the battle of Badr] with one twice as great, you said, “From where is this?” Say, “It is from yourselves.” Indeed, Allah is over all things competent.

Meaning:-
Disaster: that causes great damage or loss of life, calamity, tragedy, act of God,
Uhud: Uhud: Battle of Uhud (Arabic: ‘Uḥud) was fought on Saturday, March 19, 625 (3 Shawwal 3 AH in the Islamic calendar) at the valley located in front of Mount Uhud, in what is now northwestern Arabia.
The Battle of Badr (Arabic: ) fought on Tuesday, 13 March 624 CE (17 Ramadan, 2 AH in the Islamic calendar) in the Hejaz region of western Arabia (present-day Saudi Arabia), was a key battle in the early days of Islam and a turning point in Muhammad’s (PBUH) struggle with his opponents among the Quraish in Mecca.
Competent: having the necessary ability, knowledge, or skill to do something successfully, efficient and capable.