For most people, practicing guitar for 3 hours straight would be too much. It’s generally more effective to practice in multiple shorter sessions, taking breaks in between to rest and process what you’ve learned. Also, it’s important to maintain good posture while playing to avoid injury, which can be challenging to do for extended periods. Additionally, overly long practice sessions can lead to a diminishing return on focus and motivation. Instead, consider practicing for about 20-30 minutes, then taking a 5-10 minute break, and repeating this cycle a few times. This approach can help maintain your concentration, prevent injury, and optimize learning. However, the ideal practice length can vary depending on the individual’s stamina, concentration span, and learning style.