This question is about as old as Seneca himself. In page 10-11 (the introduction) of 'Seneca' Letters from a Stoic:

"In A.D. 58 Seneca was being attacked by people like Publius Suillius Rufus... But the campaign against him generally centered on the apparent contrast - it has been a stock criticism of Seneca right down the centuries - between his philosophical teachings and his practice."

I'm willing to go with Robin Campell's opinion on this as I'm by no means an expert. I think the circumstances of life itself lend itself to failing in your principles, reflecting and improving where possible.