Is it hard to get a residence visa in Spain?

Could you please elaborate on the complexity of obtaining a residence visa in Spain? I've heard that the process can be quite challenging, but I'd like to know more about the specific requirements and potential difficulties involved. Is it necessary to meet certain criteria, such as financial stability or proficiency in Spanish? Are there any specific documents or procedures that need to be followed? Additionally, how long does the entire process typically take, and are there any common pitfalls that applicants should be aware of? Thank you for your insights.