no such thing as free lunch

It means that everything has a cost or a trade - off. There's no situation where you get something for absolutely nothing. For example, if a company offers you a 'free' product, there might be hidden costs like your personal information being sold or you having to listen to a long sales pitch.

Another example is a free seminar. It might be free to attend, but the organizers are likely hoping to sell you some expensive course or product at the end. They're using the seminar as a way to market to you, so you're giving them your time and potentially being influenced to spend money, which means it's not truly free.

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Mysterious Tribulation.

There was a "free lunch" theorem in the field of physics. The creation of the universe could be seen as a "free lunch." In the beginning, space-time was flat and empty. Heisenberg's uncertainty principle allowed the creation of the universe in a short period of time. According to Einstein's matter-energy relationship, energy produced matter (in the form of black holes), and matter caused space-time to bend, which was gravity. The particles in the universe were created from the particle/antiparticle pair in quantum theory, but this led to the question of where the energy came from. The answer was that the total energy of the universe was zero. Cosmic matter was composed of positive energy, and the gravitational field between matter had negative energy. In the case of a universe with a generally uniform space, the negative gravitational force could just offset the positive energy of matter. During the period of expansion, the supercooled energy density of the universe remained unchanged, and the positive matter energy and negative gravitational energy doubled with the doubling of the volume of the universe. The total energy was still zero, and the total energy that could be used to create particles became very large. The universe was like a free lunch. In the field of economics, Milton friedman said,"There is no free lunch in the world." He believed that any commodity had a cost, such as labor cost, circulation cost, tax cost, etc. The producer could only make a profit by selling it at market price. If the price of the goods is lower than the market price, there must be a subsidy, which may be the government, enterprises, or others. If it was a government subsidy, the money would come from the taxpayer. It might seem free, but in reality, it was not. This kind of free lunch was actually expensive. It was the same for some commercial "free strategies". The wool would eventually come from the sheep. In terms of machine learning algorithms, there was the "no free lunch theorem." The classical theory showed that if a certain learning algorithm was better than another learning algorithm in some aspects, it must be weaker than another learning algorithm in other aspects. That is, for any learning problem, there was no optimal algorithm, only the most suitable algorithm. There was also an enhanced version. For a wide neural network, increasing its generalization performance for a given objective function would definitely weaken its generalization performance for an orthonormal function. Translated as: Palace of Pleasure, the novel is equally exciting. Everyone is welcome to click and read it!