Sale of BP

I bought BP at 379p per share in September 2011, when the oil price was $100 per barrel.  I've just sold it today at 403p per share, with the oil price under $50 a barrel.  Yes, for most of that period the share price was higher, touching 520p at one stage, so it's annoying I didn't sell earlier - but 520p is cheap with oil at $100, and 403p is expensive with oil at $50.