In the sentence-

"I`ll tell you the answer this time,but in the future you must learn to think by yourself"

I`ve chosen by, implying-"alone".

Was my choice a wrong one?

Should have I written -"for yourself" ?-meaning "independently"?

I`m totally messed up, as I can`t distinguish between these two.Emotion: thinking

I`d be very grateful, if someone cold help me.
lena_jeniI`ve chosen by, implying-"alone".
No. That makes it sound like the student should not think when there are other people around -- that before answering a question the next time, the student should go alone into a room, keep all other people out, and then think.

You should have written for yourself, that is, without help from others.

Right, I understand now the difference. Thank you very much.