James has all 100 shares in a company.
The company issues shares
The company needs more money for investment. The company issues 20 new shares to John for €50,000. The company now has €50,000 and John owns 16.6% (20/120) of the company.
Next year, the company needs more money and issues 30 new shares to Mary for €40,000.
Now John owns 13.33% (20/150) of the company. But it should be a more valuable company, because it has €40k more cash.
James sells his shares
James can sell 20 shares to John for €50k. John gets the €50k, not the company.
Later John sells 30 shares to Mary for €40k. Again, John gets the €40k. James is not affected.
But... small shareholdings in small companies are a huge source of conflict and should be avoided unless there is some huge benefit arising.
Brendan