The Precautionary Principle was formulated in the late 1960's to stop progress where there was a potential risk to health or the environment.

The principle was intended to enable people to say "no", rather than wait for the proof of danger to arrive - which may be too late. The saying 'it is better to be safe than sorry' has been legally translated via the precautionary principle.

The precautionary principle, loosely speaking, means you can reject things that are worrying. However it should not be used to stop progress without significant reason.

The UN definition (Principal 15 of Rio Declaration) says:

"where there are threats of serious or irreversible damage lack of full scientific certainty shall not be used as a reason for postponing cost-effective measures to prevent environmental degradation".

On a personal level, we may not eat eggs for the fear of getting gut poisoning, like salmonella.

Click for more on Precautionery Principle