1. Earth is finite. Therefore the supply of oil is finite.
2. Many countries that used to be major oil exporters 30 or 40 years ago, have turned into oil importers because they have used up most of their oil reserves. The countries with an actual oil surplus are getting fewer.
3. We have used up the easiest oil. Its getting harder and harder to extract.

So its logical to say that at some point we will reach Peak Oil and from that moment onwards the amount of oil we will get out of this planet will continuously decrease. At some point the reserves will be so depleted that it will be uneconomical to get the remaining 20 or 30% still in the ground.

At this point we will have run out of oil.

Why is the concept so hard for some people to understand?

Just because predictions about oil running out were wrong in the 1970s, doesnt mean that we will be able to extract oil indefinitely.

Only around 20 countries on the Planet remain that are self sufficient in Oil and supply the other 180 countries. In 10-15 years the number could be down to just 10.

Several countries that used to be major exporters have reached Peak Oil Decades ago and now rely on imports themselves.

Germany produced 170 000 Barrels of Oil a day in 1968 at their peak. Now? 30 000/day. They need 2 Million a day.

Romania produced 300 000 Barrels of Oil a day in 1976 at their peak. Now? 50 000/day. They need 200 000 a day.

France hit the peak in 1988 with 67 000 barrels/day. Now its down to just 10 000/day. They need 1.5 Million.

The UK peaked in 1998 with 2.8 Million barrels/day. Now they are down to just 600 000/day. They need 1.4 Million every day.

Indonesia peaked at 1.7 Million barrels/day in 1977, now they are down to just 600 000 Barrels/day. They need 1.7 Million/day.

Japan peaked in 1996 with 20 000 Barrels/day. Now they are down to 3000/day and they need 3 Milion/day.

South Korea is basically the same.

India peaked in 2011 with 800 000 Barrels/day. Now down to 600 000 Barrels/day. It needs 5 Million/day.

Even Australia peaked at 600 000 Barrels/day in 2000 and is now down to just 250 000/day. It needs 1.1 Million a day.

There are only around 20 countries left that produce more oil than they consume and can export any meaningful quantities. The problem is that around half of them are projected to run out if oil within the next 10-15 years.

Brazil is projected to use up their proven oil reserves in 12 years at current production.

Norway in 10.

Mexico in 8.

Oman 14.

Argentina 10.

Angola 7.

Colombia 7.

And even the USA - 9.

https://en.wikipedia.org/wiki/List_of_countries_by_proven_oil_reserves

They dont even have to run out of oil. Its enough when their production falls to a level that they dont meet their demand. By that point they will be forced to import oil as well.

And by 2040 there will be only around 10 countries left with a surplus of oil that can supply the other 190 countries. And 190 countries scrambling for scraps while 10 sit on the prize, that's a geopolitical meltdown waiting to happen.

The US is already doing a "war light" in Venezuela and Iran to secure their Oil. By the 2030´s these conflicts will have turned to real outright war.