Beginner here learning: why can the king not simply take the rook here?

The rook is defended by black king. Moving the king to dangerous square is illegal move.

In this position, the king on the square f5 is guarding the rook on g4. The white king can't capture the guarded piece.

Oh okay so the Black King could capture the white king if it took the rook? I assumed as much because it's very obvious but I googled it and somehow got the answer that the king cannot directly capture the opposite king so I was confused
sorry if it seemed dumb but I'm leanring thanks

Its guarded by the white king and u cannot place ur king in a square where it can be captured

King can capture King.

In Vietnam, and America, I played chess with hand-me-down rules from the kids in the neighborhood.

So the rules were incomplete.

There is no announcing "check" rule.

A King can be captured like any other piece.

I did not know it, I was playing with the original rules of chess.

The modern rules of "sportsmanship" needlessly complicate things.

When in doubt, treat the King like any other piece. The King has no privileges.

That will also solve your questions about what is a pinned piece.

Not a good advice. In all chess games following the FIDE rules, the king can't be captured, and it also can't be allowed to be captured. A check is always a check.

Then FIDE rules suck.

There is only 1 rule, in chess and in life. A rule is a rule if it is agreed by two people. The two people playing the game.

Put on you thinking cap.

What is the real difference between "FIDE" rules and my "home" rule which was the historical rule?

Nothing.

The "home" rule, the historical rule, is the clarification of FIDE rules.

On the platform Meetup.com, we play chess face-to-face in a "brewpub".

Of course, "the young ins" are weaned on Internet speed chess. They play 5 minute games.

I came from a real chess club. Time control was 90 minutes for 40 moves + 60 minutes.

My rule is 60 minutes on the clock or I will not play.

The people who do not agree to it, even they respect it.

Same in life.

Like marriage.

It's rules 2 people agree on.

I ran a tennis Meetup, Meetup.com.

I count like ping-pong to 21 points. 1, 2, 3 . . . 21. Just like the Count on Sesame Street.

I need to count that way to establish Elo ratings.

Tennis scores are not tennis "scores".

A game could be 1,000,000 to 1,000,002. You cannot re-construct the game.

A stupid Black woman wants to count the "tennis" way.

love, 15, 30, 40, deuce, ad in, and out, game.

What the hell is that?

She quit the tennis Meetup.

Just as a well.

On the Yang side, I would have kicked her out of my tennis Meetup.

Sometimes abbreviated as

love, 5, 3, 4 . . .

What?

Countig like ping-pong, each persn seraves 5.

We have 2 hands of 5 fingers each. That is why we have a 10-base system, decimal.

Serving on the right hand side, there is an unequal number of right versus left serve, modeled on chess, more King side castling than Queen side castling.

I call it "neighborhood rules."

A guy asks, "What kind of neighborhood is this?"

me: My neighborhood.