New things tend to be, by default, risky because limited evidence exists as to their full consequences. The precautionary principle is to remain skeptical and cautious of things that may have significant consequences, especially as some might be hidden and currently unforeseen.
The general idea is that when you change or add something, you introduce complexity, and we usually cannot predict all the results of this complexity. So there should be strong evidence or reason for change, otherwise the potential negative results may overweight the positives.
Consider that your friend recommends you stop eating meat and take in your protein in the form of insects instead, for ecological reasons. The precautionary principle here would have you question this recommendation, given the health impacts of meat consumption are known but the impact of insect consumption at big portions isn't.
Yes, you may receive the same amount of protein, but you would introduce significant change to the enormously complex system that is the body, so there are likely to be hidden consequences. Some of them might be positive, some disastrous, or maybe everything would be fine - we don't know!
The precautionary approach doesn't necessarily mean you're "stuck in your ways", never try new things and never innovate. Rather, it's a more risk-averse approach at trying new things and innovating; perhaps a more humble way to do things, as you appreciate the limits of human knowledge amid vast complexity.