def _add_legend(axis1, lines, legend):
    """
    Function to add a legend to a Reliability Growth plot.

    :param list lines: the list of lines to add to the legend.
    :param tuple legend: tuple of legend text.
    :return: False if successful or True if an error is encountered.
    :rtype: bool
    """

    # Create and place the legend.
    _leg = axis1.legend(lines, legend, loc='best', shadow=True)
    for _text in _leg.get_texts():
        _text.set_fontsize('small')
    for _line in _leg.get_lines():
        _line.set_linewidth(0.5)

    return False