Shifting threat of substitution. The most common reason substitutes become more or less threatening over time is that advances in technology create new substitutes or shift price performance comparisons in one direction or the other. The earliest microwave ovens, for example, were large and priced above $2,000, making them poor substitutes for conventional ovens. With technological advances, they became serious substitutes. Flash computer memory has improved enough recently to become a meaningful substitute for low-capacity hard-disk drives. Trends in the availability or performance of complementary producers also shift the threat of substitutes.