Ask HN: Is it crazy to get a co-founder? 50% seems a huge price to pay

OK say you are a technical single founder and you have built your product.

All the advice is to get a co founder, but usually that means 50% ownership right?

Seems a high price to pay when getting an injection of capital might only cost 20% of the company.

If you are a technical single founder with a completed product, wouldn't it be crazy to get a sales oriented cofounder at 50% of equity?