てしょうがない/てしかた(が)ない, "You shouldn't"

Question

As far as I know, forms like 「てしょうがない」 and 「てしかた(が)ない」 means something like "very, extremely" and "can't be helped", like:

心配する理由はなかったけど、どうしても不安でしかたなかった: I didn't have any reason to worry, but I couldn't help be uneasy

Then I found this sentence:

そんな本は読んでも仕方がない

which was translated as "You shouldn't read a book like that", while I translated it as "I can't help reading a book like that"; there is no context, it's an example sentence from a grammar.

I know those form can also mean "There is no point in doing something", but I'm not sure how to discriminate between those meanings. After reasearching a bit, I thought the difference was in the 「も」: 「てしかたがない」, "I can't help but"; 「てもしかたがない」, "I shouldn't". The again, I just found this sentence:

こんな酔っぱらいと時間をつぶしたってしょうがない

which to me sounds like "I couldn't help wasting time with such a drunkard", while it was translated as "I shouldn't have wasted time with such a drunkard", without having 「も」. I'm wondering if 「たって」 is a colloquial form for 「ても」: I know some time ago I found such a case, but I can't find it anymore.

I found some questions here about these forms, but nothing addressing this; in my grammar and on the Internet all I can find are the meaning I gave above, with no explanation about the "You shouldn't" meaning. I did find this page, in which there are examples like 「まだ証明されていないことを考えてみても仕方がないぜ」, translated as "Do not spend thoughts on a matter which has not been proved", which seems to prove my point, since it does have 「も」.

Am I missing something? Am I right in my 「てしかたがない」, "I can't help but"; 「てもしかたがない」, "I shouldn't" interpretation? Is it just depending on context?

Answer 1

I think you're right. ～てしょうがない/～てしかたない (without も) can mean "(I) can't help but...", and ～てもしょうがない/～てもしかたない, "(You) shouldn't..."

And you're also right that ～～たって (<た+とて) is a colloquial way of saying ～～ても, "even if".

So these phrases are literally like...

• [感情・感覚を表す表現(phrase expressing feeling or emotion)] + て(で) + しかた(が)ない/しょうがない/しようがない (or たまらない/ならない)
  → "I want/feel... + and + nothing can be done about it (←the feeling)." → "I can't help feeling..."

• ～ても/～たって + しかた(が)ない/しょうがない/しようがない
  → "Even if (I/you) do~~, + nothing can be done about it (←the situation)." → "There's no point in doing..."

Examples:

• 心配で仕方なかった。 I couldn't help worrying. / I was really worried.　
• 心配しても仕方ない。 There's no point in worrying. / Don't worry.
• あの本が読みたくてしょうがない。
  I can't help but want to read that book. / I wanna read that book so bad.
• そんな本、読んだってしょうがないよ。
  There's no point in reading a book like that. / You shouldn't read a book like that.