I've seen in the Lego LEGO Shop at Home this tag that identifies some items In this category there are some old sets but some new sets too, like 10226 Sopwith Camel and 10220 Volkswagen Van what's the meaning of this category? "hard to find" because they produce not a lot numbers? Is it right to consider to invest for this reason?

I think you can ignore the "Hard to find" tag, see the situation of eg. 10197 FB and 10188 "Live Star" and you'll know what I mean.

I've seen in the Lego S@H this tag that identifies some items

In this category there are some old sets but some new sets too, like 10226 Sopwith Camel and 10220 Volkswagen Van

what's the meaning of this category? "hard to find" because they produce not a lot numbers?

Is it right to consider to invest for this reason?

In lego's printed catalog, "hard to find" is defined essentially as items that can only be purchased at lego and selected retailers (e.g. 6857 - joker's funhouse can only be found at lego and TRU in the US)

LEGO's tags are becoming increasingly silly. As mentioned above, "hard to find" refers to exclusives. If you are looking for a set that is only sold in the LEGO Stores, but the closest one to you is six hours away, that set is indeed going to be hard for you to find. I'm not sure what the motivation is for that tag. As for the "retiring soon" tag, no one even really knows what that means yet. This is a newer tag, and seems to be applied only to random sets, not ALL sets that are reaching the end of their run. Silly LEGO tags...

LEGO's tags are becoming increasingly silly. As mentioned above, "hard to find" refers to exclusives. If you are looking for a set that is only sold in the LEGO Stores, but the closest one to you is six hours away, that set is indeed going to be hard for you to find. I'm not sure what the motivation is for that tag.

As for the "retiring soon" tag, no one even really knows what that means yet. This is a newer tag, and seems to be applied only to random sets, not ALL sets that are reaching the end of their run. Silly LEGO tags...

Someone mentioned in a thread (can't remember where) that there is a theory as to why Lego uses "retiring soon" tag for some sets and not others.

In some cases, Lego wants to retire sets, but have excessive inventory that they want to get rid of, they would put that tag up in hopes to have inventory reduced significantly.

I think that theory has some credence. In our past observations, has the "retiring soon" tags been used on sets that aren't exactly popular?