How do potential substitutes threaten sales in an industry? Illustrate your answer with specific examples.

Ease of substitution strongly reduces an industry's attractiveness and profitability.The threat of substitution is high when an alternative offers an attractive price-performance trade-off and when there are low switching costs to the buyer.".pf" is a threatening substitute for print forms,and it strongly reduces demand in the printing industry.Voice-over is a strong substitute for mobile and fixed-line telephones.