It's not perfect, as others have already said, but if you study the types of failures that can occur in the Bitcoin ecosystem, you'll notice that these are problems with very low probabilities of happening, and most of them requiring astronomically high computational power to happen.
It is quite noticeable that Bitcoin also suffers on ups and downs in terms on its system. But it is normal to happen because Bitcoin as form of crypto-currency is a developing current which in tend to experience a good history of development for it to have a secure transaction. So if you are going to support Bitcoin and used it as a form of daily transaction more development, growth and progress could actually happens more to bitcoin system and security to make it a more secure in terms of transactions.