[ADVICE] I love my job; the work is super interesting. But some days are worse - I can't get anything done by EOD and I feel very guilty about it.

I am a software engineer. I work for a huge (and successful) technology company in US. People here are super talented. I always try to perform well and accomplish quarterly goals. I love my work a lot. But some days I just can't get the work done. I come home assuming I will finish my tasks by night and I just do nothing. That puts me behind the schedule. I feel guilty for it sometimes. My goal is to perform well every single quarter.