For starters, lenders are legally obliged to check that you can afford their mortgage purely on today’s income before they lend to you.
However, your income is usually not static over time. For most people, it goes up over time as you get promoted or find other ways to earn money investing etc. Not only that, your interest payments also typically go down over time as your balance owing falls. This means that all else being equal, the mortgage payments get far more manageable over time. It’s only toughest in the first couple of years.
The whole point of being in debt is to bring forward the purchase of the house as most people won’t have the cash to purchase it upfront (and you get to ride the appreciation in value of the house earlier). If the idea of being in long term debt scares you, then good luck trying to buy a house with cash upfront.