The Cherries had the lead through an own goal from Vitaly Janelt own goal, before the Bees fought back through Yoane Wissa and Christian Norgaard.
“At the end, I think it's another of these games where we are not efficient,” he said.
“We are not efficient and I think we are doing a lot of very good things. But the most important things, there are other teams that are doing much better than us. And set play goals are valued the same.
“Obviously we know Brentford, we already conceded one long throw in when we faced them there. We've been working on it.
“But at the end it's a matter of leaving the second ball, smelling the danger, reacting quicker than them. They've been better now in set plays, I think we've created more chances. We will now check the stats and we will have more of everything.
“But when it happens, not only today, because if it's only today, you say bad luck. We had the crossbar chance, the keeper saves it over the line, a small offside, not a penalty, small margins.
“But when it's happening, especially in the last games, I would say almost every game we need to improve in the boxes, it is what it is.”
On trying to bounce back, Iraola said: “It's obviously hard work, but it's just also the mentality, the ruthlessness of valuing every chance. It's not like, okay, I have a chance in five minutes, I will have another and we will continue arriving.
“Sometimes it's not possible. So you have to value every chance. And I think today they were more efficient at the end.”