Why do we need to deduct gain on sale of plant assets from net income to arrive at net cash flow from operating activities

The money received from the sale of assets is included in the net cash flows from investing activities, that is why you must adjust net income by eliminating any gain or loss resulting from these transactions.  

Explanation:

E.g. net income = $50,000, and it includes a gain of $5,000 resulting from the sale of a truck. The truck had a book value of $15,000, but was sold at $20,000.

Net cash flows from operating activities:

Net income $50,000

Adjustments to net income:

- Gain on sale of asset ($5,000)

Net cash flow provided by operating activities $45,000

Net cash flows from investing activities:

Sale of truck $20,000

Net cash flow provided by investing activities $20,000

d, conspicuous consumption is when you try to increase your wealth or social status (and in the case he's trying to create the perception of wealth considering he can't really afford it)