The first is that the person thinks that the NPV of the future cash flow generated by this investment is higher than the current asking price. I call this rational value analysis. The second is when an investor buys a security under the assumption that some person in the future will buy it from him for a higher price regardless of any underlying value or future cash flow stream. This is the increase in value of your company, in today's dollars, if you were to make the investment and achieve the cash flows as estimated. The most important concept to learn about the Value Curve is the relationship of Value and Discount Rates.
Value decreases as interest rates increase.
Likewise, value increases as interest rates decrease. One warning about choosing a discount rate. Do not fool yourself into believing that you are neutralizing risk by arbitrarily increasing the discount rate. Raising the discount rate does not change the probability of any particular adverse event happening. Risks should be analyzed separately from the determination of the proper discount rate.