La Masia graduates Carlos Perez and Ansu Fati struck for the 2-1 triumph to condemn Inter to the Europa League.
Valverde said, "You can think about how a game will go, but you ultimately don't know for sure what will happen.
“Inter pressed us well early on and kept us pinned back, but we emerged over time. I think they were increasingly irritable because the goal wasn't coming and they had three ruled offside, so it got to them."
On Inter, the coach added: Inter without doubt are good enough to go through to the Champions League last 16, as they played so well for example in the first half at Camp Nou and then in Dortmund.
“I think the anxiety of the goal that wasn't coming in the second half got to them and affected their performance."