It seems that God is very forgiving; what is the significance of "Beware of small sins"?

I get the impression that God is always ready to forgive, giving lots of leeway and many chances to repent. Below is an example of what I mean; I see comments like this all over the place in the Qur'an: > 25:70 ...save him who repents, and believes, and does righteous work -- > those, God will change their evil deeds into good deeds, for God is > ever All-forgiving, All-compassionate; In Tafsir ibn Kathir, for [Surah 54, near verse 55](http://www.alim.org/library/quran/AlQuran-tafsir/TIK/54/47) (the verses in the online tafsir are hard to identify), Muhammad says to Aisha: > "Beware of small sins, because there is someone assigned by Allah who > records them" I have questions: * Is this from a hadith? I couldn't find the phrase anywhere online * Does God treat small sins differently, such that repentance is not enough to obtain forgiveness? * Does God hold people accountable for repenting from small sins in detail, or is it enough to ask forgiveness for unknown small sins? * What counts as a small sin? * Any other useful or related information would be awesome