We can sin intentionally or by mistake. Sin is deeply ingrained in humans and creates a barrier between them and their Creator.
وَتَجْعَلُنَا نُخْفِقُ فِي بُلُوغِ غَايَتِنَا ،‏ تَمَامًا كَمَا يُطْلِقُ ٱلرَّامِي سَهْمَهُ دُونَ أَنْ يُصِيبَ هَدَفَهُ .‏