Often no reason is given for not being allowed to do something e.g. why are we not allowed to read theillim at night ? A reason would give us more conviction when fulfilling mitzvot

Shalom, I totally agree that the more one understands something the greater connection they will feel, and the greater conviction they will have when doing the mitzvah. We try, within the limits of the media of short internet answers, to both answer the "bottom line" question at hand, and still provide an understanding of the underlying subject. In relation to the question at hand - the question was a follow-up to a previous question which did in fact give greater background to the issue. If you check the earlier questions and answers (search "tehillim" on the site) you will see that the reason for those who do not say psalms at night is based on the midrash that Hashem taught Moshe written Torah in the day-time, and Mishna (oral Torah) at night - indicating that the night time is more fitting for the learning Oral Torah than it is for saying Tehillim, which come from the written Torah. None the less, the Rabbi there ruled, as did I in a later response, that one may in fact say tehillim at night. (See the earlier responses for our reasoning). Blessings, D. Sperling.