"Limping always bad?" No.
Any statements, or questions, with absolutes like "always" or "never" are usually not correct. Some things are indeed absolutes, but most things (especially in poker) have exceptions.
Is limping ALWAYS bad? No. Is it usually bad? Yes, it usually is worse than open-raising.
The primary problem with limping is that you allow others into the pot after you for a cheaper price - even if you have a powerful hand like the mighty AA, you are still vulnerable to combined equity from many players after you.
Similarly, limping is also "bad" in the sense that it limits how many "ways" you can win the pot. If you open-raise, there is a chance that everyone will fold and you pick up the pot (can hardly complain with the good result of winning a pot preflop and especially so with rising blinds or even an ante in play). However, if you open-limp (or limp behind), then there is no chance of anyone after you folding, unless someone raises after you act and now you are not the aggressor (and likely out of position now as well).
To illustrate as example of even the mighty AA hand vulnerable to
equity from many players, here is an example of holdings with their equity:
Hero (BTN): Ah Ad - 62.57%
SB: Js Ts - 21.34%
BB: 7c 2c - 16.09%
These percentages are calculated by simply putting these
hands into the
free poker calculator Equilab.
In this example, our Hero had the best preflop hand possible while on the Button. Instead of open-raising, they open-limped and the blinds stay in the hand. This is just one sample of holdings, but here we see how even pocket Aces are only winning a little over 60% of the time in this multi-way pot. Even 72 (although suited) is winning about 16% of the time here!
Now imagine we were to open-raise instead. Most likely, at least one player would fold and perhaps we could take the pot right here. Let us say we open-raise instead and the 7c 2c hand in the Big Blind (BB) folds.
Here is our new equity with Ad Ah vs Js Ts:
AA - 78.28%
JTs - 21.72%
This example (with a heads-up pot or with 3 players going to the Flop) had our Hero on the Button (BTN), but what if we weren't so lucky?
In that scenario, it is likely others after us will limp behind and now we are in a multi-way pot with one or more players having position on us! This is just a scenario (or a few) which hopefully convey why limping is often discouraged. Is it ALWAYS bad? No; usually, yes.
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