Here are a few examples of fine-tuned physical constants and their importance:

• Electromagnetic force constant - Also known as the fine-structure constant or Sommerfeld's constant and symbolized as the Greek letter alpha (α). The electromagnetic force governs electrically charged atomic particles (protons and electrons). Its value is important for the existence of stable atoms, and by extension, chemistry and life. If α were significantly larger: The electromagnetic repulsion between protons in atomic nuclei would be so strong that nuclei could not hold together, making atoms unstable. No atoms would mean no molecules, planets, or life.^{[1] [2]} If α were significantly smaller, electrons would be less tightly bound to nuclei, making atoms and molecules unstable in different ways and complex chemistry required for life would not be possible. ^[2:1]
• Strong nuclear force constant - It is commonly referred to as the strong coupling constant (symbol: αs), quantifies the strength of the strong nuclear interaction, which binds protons and neutrons together in atomic nuclei. If αs were slightly weaker (about 2%), the force would not be sufficient to bind protons and neutrons together so only hydrogen would exist. Heavier elements, such as carbon and hydrogen, would never form. ^[3] If αs were slightly stronger (about 2%), protons and neutrons would be bound so tightly that all hydrogen atoms would be converted into helium and heavier elements very early in the universe. This would leave no hydrogen for water and no long-term fuel for stars, both of which are crucial for life. ^[3:1]
• The ratio of the mass of protons to electrons - If this ratio (~1836.15) were significantly larger or smaller, electrons would either move out away from their orbitals and not spin around their nuclei, or be too tightly bound, and prevent chemical bonding.^[4] The formation of molecules could not occur and the formation of molecules such as water and DNA would be prevented. Over 98% of a proton's mass comes from strong-force binding energy, not quark^[5] masses. However, the up- and down-quark masses must still fall within narrow ranges to ensure stable protons and neutrons.^{[6] [7]}
• Ratio of mass of protons to neutrons - The mass of neutrons is slightly larger than the mass of protons. If this difference was smaller, protons would decay into neutrons, thus preventing the formation of hydrogen for water and organic molecules. If the difference was larger, neutron decay would destabilize atomic nuclei. ^[8]
• Tides and Stabilization of the Earth’s Tilt Caused by the Moon - The moon stabilizes the earth’s tilt on its axis at about 23.5 degrees, which allows us to have relatively consistent seasons. Also, the moon is responsible for tides, which create tidal marshes for various animals. Tides also circulate nutrients in the ocean, benefitting ecosystems by distributing nutrients and oxygen to different areas.
• Earth’s size is just right for creating a magnetic field that protects us - The movement of molten iron and other metals within the earth’s core creates a magnetic field around the earth called the magnetosphere. The magnetosphere protects the earth from the solar wind from the sun that would strip away our atmosphere and harm organisms. By having a sufficient mass, the Earth is able to retain enough internal heat to keep its core partially molten. This moving molten core powers the geodynamo, the process that generates the magnetic field.^[9]. If the earth were much smaller, like Mars, its core would cool faster and solidify, resulting in a magnetic field that is either weaker or non-existent. If the Earth was much larger, the internal pressures and compositions might differ, affecting the nature of the core and the geodynamo process.
• Earth’s distance from the sun is just right for life - The earth’s distance from the sun is about 93 million miles (150 million kilometers). This distance allows liquid water to exist on the Earth, which is necessary for life. The Earth’s habitable zone, the distance between the earth and the sun where liquid water can exist is between 0.95 and 1.4 Astronomical Units (AU). One Astronomical Unit is the actual distance between the Earth and the Sun (~93 million miles). If the earth was much closer to the sun than 0.94 AU, it would be too hot for stable climates and plant life. If the earth was farther than 1.4 AU, there would be extensive glaciation.

Footnotes