Opportunity discovery and opportunity creations are theorized under certain assumptions (Alvarez, 2005). However, the majority of researchers takes either of these assumptions as granted.
Uncertainty and risk in a given environment can be studied in context of the strategic posture of the firms. For prospective type of firms (Prospectors), uncertainties and risks are opportunities and they tap first and become the leader in the market. Inversely, for analysers, followers, and reactors these remains as risks and opportunities. Prospectors convert every risk and uncertainty into opportunities.
If the existing need is identified then it is opportunity discovery, but creation/ innovation without referring to existing need, may in future create opportunities(Supply creating its own demand). Uncertainty may come from the feasible-desirable-capable perspective.
Coming to the question of "how often", entrepreneurial effort would be more towards "Opportunity discovery" rather than "creation/ innovation"