Missed Opportunities II

I should do one of two things.

Either a) give up playing chess or b) improve my calculation and vision.

Here is where I, as Black, reached on move 26 against a higher-rated opponent....

How did I miss it ?!

I'm sure, dear readers, that you can see the obvious move.

I did too, but missed a vital part of the combination as it was outside my vision. [ See the comments ]

Is there a chess maxim that you should always play a check ?

Enjoyable, none the less, although I'm a little aggrieved that I made my losing move after my opponent started to talk to me and interrupted my concentration.

I would have lost on time anyway, but next time I will play in silent mode !