In my way of thinking, you've muddled a couple categories... Overall, if I bought a big stake in one company and it went up from 15% of portfolio to 27 I'd be selling some!
The House being a big % of net worth is a bit of a different animal as you need a place to live. Owning a home gives you lifestyle security in a place you want to live. Arguably with insurance, it will never go to zero in value. (even if housing prices drop substantially, if you are in a place you want to live, its always worth that to you). At the same time, if your house doubles in value that doesn't mean much if you really don't want to move.
If you own a company it is reasonable to have a big % of your worth tied up in it. As an owner, you control the decisions. With company's you've invested, your info comes after the fact in the 10k and you likely do not have access to real insider information. Which would of course be illegal to trade on, yet how many stocks to you see move before news?
For zesty things and individual equities, I limit to 5% of total Portfolio / 10% of the portfolio for such things. (I look at portfolio only, exclude the house). As things go up I slowly sell to maintain this, I've missed some home runs this way and avoided some real disasters too. You don't mention if this is in taxable or pre-tax accounts... the tax man takes his share of your winnings and you get to pay for your losses. Maybe you can carry a loss forward but if your gains and losses don't neatly fall into tax years to offset, taxes can affect the risk/reward trade off you may think you're making.
For those with restricted holdings in an employer's stock, I don't necessarily value those at full market value until they become unrestricted. They are hope and potential and may well be worth working for, but are not yet net worth.