Changes in temperature, humidity or heavy use will make it necessary for more frequent tunings. If a piano is not given regular tunings, the instrument will be more unstable.
It is difficult for a technician to hold tune a neglected piano; some times, it is more costly to restore the neglected piano to hold tune than if it had been kept under regular and constant care.
Unfortunately, no matter how expertly a piano is tuned, atmospheric variations and the nature of the piano's construction constantly conspire to bring it off pitch.
Your piano will perform best under consistent conditions neither too wet or dry, optimally at a temperature of 20 degrees C and 42% relative humidity. Dryness causes the piano's pitch to go flat; moisture makes it go sharp.