LOL...that is not a simple question
Without going into fluid dynamics, you have to understand how an open bearing (like rod and main bearings) work. In a simple sense, the bearing "water ski's" on a wedge of oil as the journal rotates. The oil is pumped in and exits out the bearing sides...it has to be constantly replenished to provide the volume of oil required for film thickness in the bearing. A secondary, but very important, function is to keep the bearings cool. This pic might help visualize it:
What's important is the volume of oil supplied, not the pressure...flow is going to give you the greater volume and is dependent on the size of the pathways. Pressure (you can look at it as flow rate) will too, but only to the point where the oil channels in the block, crank, etc can handle that volume. Once that point is reached, you have very little additional flow for a much larger rise in pressure. This is why you will hear "pressure is resistance to flow". Higher viscosity oils have an intrinsic resistance to flow...thicker fluids are harder to move through a given size channel.
Keep in mind this is the simple version explanation...it's really a lot more complicated than this.
BTW - There is a fair amount of particulates floating around in your oil...soot from combustion, particles your air filter misses, etc. You oil carries this crap to your filter so it can be removed.