I wasn't a beginner, but I did it anyway. In about 1978, I decided to go to Big Sur and spend two days traveling its length, stopping at every turnout on the road. I had been there before, but never with that kind of time. I had my usual Kodachrome 25 and 64 with me.
Partway through, I switched from K64 to K25 and forgot to change the ASA dial. I usually exposed at nominal film speed, though their tolerance for underexposure meant I knew I could get good pictures even when the meter said I couldn't, especially at sunrise or sunset. But this happened at midday. So I accidentally underexposed the K25 by 1 1/3 stops, thinking it was nominal. I was very upset with myself when I realized it. If only I'd compared the exposure settings to the conditions and film speed... but I didn't.
When I got the pictures back, I was stunned. The underexposed K25 was gorgeous! The colors had saturated as only Kodachrome could, deep and rich- more intense than reality, certainly, but still very real looking. The blue of the water took on a depth I'd never seen. The images were of the cliffs and sea, and the lack of shadow detail just made the cliffs look more dramatic. The sense of a very bright, clear day was portrayed better. My mistake turned into a delightful and fascinating discovery.
God I miss Kodachrome.