A typical complaint amongst club players is that they don’t have enough time to study theory, though usually it isn’t the opening that’s the problem. The feeling of not knowing the opening usually stems from not knowing what to do after the opening, which is usually a lack of middle game understanding.
Of course things don’t get better if someone then spends what little time they have for chess on opening moves rather than investing them in more profitable aspects of chess. It’s better to play fairly simple schemes in which there are clear plans.
Here’s an example of a simple looking opening which can nevertheless by very dangerous in the hands of a good player. In this case it’s the German Grandmaster Ralf Lau who provides an object lesson in the art of tactical play with a series of hammer blows starting with 14.Re5!: