When the Moon, Mercury and Jupiter are strong and are favourably placed in a chart, the native will definitely have sound mind, sharp intellect, healthy reasoning and mature wisdom. If they are not well placed (placed in 3rd, 6th, 8th or 12th from ascendant) or are afflicted by a malefic planet such as Sun, Mars, Saturn, Rahu, Ketu then there could be chances of the native not having the mental faculty well balanced as indicated by the planet.
For example - In case of above afflictions to Moon, the person can become highly imaginative, or paranoid, or depressive.
In case of Mercury, the native can lack intellectual balance, be nervous and lack general public behavior.
In case of Jupiter, the person can lack wise decision making skills and any propensity towards higher learning or traditions. The person can also display inability to take wise decisions and implement them.