Countable AND Uncountable (?!)
Moreover, a failure can be caused by a lack of practical experiences.
It's annoying, I know, but while some nouns are countable and others are uncountable, yet others can be either countable or uncountable, and here are two examples in the same sentence: failure and experience.
Generally speaking, if a noun can be either countable or uncountable, and if you're speaking generally, use the uncountable form.
On the other hand if you're talking about specific things then use the countable form - for example you may be talking about the time you failed an exam and saying what a terrible experience that was.
In the original example, I think we're talking generally:
Moreover, failure can be caused by a lack of practical experience.
Other posts on GuruEAP examine other words that can be either countable or uncountable: