Like probably everbody I have a hard time with Keigo. I get the basic concept of in-group and out-group and neutral-group but I am really confused about switching between 丁寧語 and 謙譲語 when talking about things that I would count to in-group matters because the concern me in some way.
For example I was told that if you introduce yourself in a job interview, you wouldn't use 謙譲語, so you would just say 来年卒業します instead of 来年卒業致します。Is that because you would lower your university with you? But if I google it, I find results saying 卒業致します... x.x
Also when my boss asks me about where I went for holidays, to answer スペインに行って参りました。sounds "good, but very polite" according to a Japanese friend of mine and he meant that just スペインにいってきました。 would be better. But he couldn't tell me why... x.x Is it because, if my boss asks me a somewhat personal question or wants to have small talk with me, it's already a signal that he wants a more relaxed atmosphere and I am allowed and supposed to answer in just 丁寧語？
And one last situation. When asked by my boss if I could finish something until noon, I was told it's fine to just answer はい、できます。or はい、間に合います。 instead of something like はい、お仕上げできます。 It's not considered belonging to the neutral group if someone asks me if I am capable of doing x, is it? But then why…
I am so confused ... x.x