Think of 'buy into' as metaphorically 'buying' or accepting an idea as you would purchase goods.

Metaphorical Purchase

The phrase often implies emotional investment along with intellectual agreement.

Emotional Investment

Use 'buy into' in informal discussions when expressing agreement or belief.

Focus on the financial aspect; it involves investing money in a venture.

Understand that 'buying into' a company means you're acquiring a piece of its ownership.

It suggests a long-term involvement in the business, beyond just a quick win.