I don’t think I have heard of shiflus before. You said it means lowliness and that it’s also bad, like gaava is bad. Please tell me more? Which is worse, gaava or shiflus? If you have to err on one side or the other, is it better to risk having gaava of shiflus?
Shiflus is a feeling of lowliness, and a feeling that one is worthless, useless, low etc. The baalei mussar say that shiflus is worse than gaavah, because gaavah is a specific issue that he person has to take care of, but shiflus on the other hand ruins the persons will and capabilities to grow and accomplish what they have to in this world. Therefore shiflus is worse. I heard R’ Volbe zt”l quoting R’ Yeruchum of MIr zt”l a number of times, that a person that doesn’t know their chisronos (their faults), then the person doesn’t know what to fix, ( which is a local problem) however if the person doesn’t know his ma’alos (positive, strong points) then they don’;t have the the tools with what to fix! Therefore shiflus is worse than gaavah.