Missing the Obvious

This unfortunate mishap comes in different flavours. There might be a piece to be captures, or you've left a piece undefended, or there something devastating one move ahead, all of which you failed to see. This is often referred to as chess blindness, but I find that term misleading. It has nothing to do with poor vision, and blindness seem to imply that there's nothing to do about it. Of course there is! What's happening here is that your mind lures you to focus on something else (using blindfolds as a primary tool). If you allow that, bad things will inevitably happen.

This example starts out as a case of lack of knowledge. 

N.N. - Me (Open Tournament, 2022)

1.e4 e5 2.Nf3 Nc6 3.Bb5 a6 4.Ba4 Nf6 5. d4 The Mackenzie Variation. It's an old line, not considered very promising for White. The mail line goes 5...exd4 6.O-O Ne7 with an equal game, but I didn't know that. 5.Nxe4 6.Qe2 This looks strong, but Black has good survival chances in the complications following 6.b5. Instead, I decided to retreat the Knight, completely missing the capture on e5. 

6...Nf6  7.dxe5

Though equal in material, Black is now completely lost. The best move now is 7...Ng8, admitting that the Knight has wasted four moves on absolutely nothing. Instead:

7...Nd5 8.Bb3 Nf4

Finally an active move, hitting both the Queen and g2. However, the capture Bxf4 puts the misfortunate Knight to rest.

That was two times missing the obvious in the course of just eight moves, all because I didn't know the Ruy Lopez well enough. Even if you're unfamiliar with the somewhat obscure Mackenzie Variation, you should be able to play 5...4xd4 on basic principles alone.

Takeaway

There are two lessons to be learned here:

When you go into a Big Think, don't play the move you come up with immediately. Sit back, take a deep breath, and take a fresh look at the position. Are there any obvious captures or threats that you have overlooked?

Also, don't play openings you don't know. There's a choice here - learn them properly, or avoid them altogether.